# Problem preserving indexes using Query.jl and IndexedTables.jl
**URL:** https://discourse.julialang.org/t/problem-preserving-indexes-using-query-jl-and-indexedtables-jl/3650
**Category:** General Usage
**Created:** [May 11, 2017, 4:06pm UTC](https://discourse.julialang.org/t/problem-preserving-indexes-using-query-jl-and-indexedtables-jl/3650 "2017-05-11T16:06:42Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@merl-dev](https://discourse.julialang.org/u/merl-dev)
#### Post date: [May 11, 2017, 4:06pm UTC](https://discourse.julialang.org/t/problem-preserving-indexes-using-query-jl-and-indexedtables-jl/3650/1 "2017-05-11T16:06:42Z")
When joining 2 IndexedTables some of the data columns end up as indexes. Am I missing something here, or is this an issue:
```julia
julia> using IndexedTables, IndexedTables.Table, Query
julia> dt1 = Table(Columns(id = collect(1:5)), Columns(var1 = rand(1:2,5), var2 = rand(5)))
id │ var1 var2
───┼───────────────
1 │ 2 0.353364
2 │ 2 0.995482
3 │ 2 0.174313
4 │ 2 0.833255
5 │ 1 0.20114
julia> dt2 = Table(Columns(id = collect(1:5)), Columns(var3 = rand(1:1000,5)))
id │ var3
───┼─────
1 │ 42
2 │ 682
3 │ 615
4 │ 942
5 │ 864
julia> @from i in dt1 begin
@join j in dt2 on i.id equals j.id
@select {i.id, i.var1, i.var2, j.var3}
@collect Table
end
id var1 var2 │ var3
───────────────────┼─────
1 2 0.353364 │ 42
2 2 0.995482 │ 682
3 2 0.174313 │ 615
4 2 0.833255 │ 942
5 1 0.20114 │ 864
julia> Pkg.status("IndexedTables")
- IndexedTables 0.1.2 master
julia> Pkg.status("Query")
- Query 0.4.0+ master
```
---
### Author:  [@davidanthoff](https://discourse.julialang.org/u/davidanthoff)
#### Post date: [May 11, 2017, 4:55pm UTC](https://discourse.julialang.org/t/problem-preserving-indexes-using-query-jl-and-indexedtables-jl/3650/2 "2017-05-11T16:55:24Z")
The final `@collect` statement in this query is essentially just a shortcut for passing the same query (without the final statement) to the `IndexedTable` constructor. So you can think of this query as being equivalent to:
```julia
q = @from i in dt1 begin
@join j in dt2 on i.id equals j.id
@select {i.id, i.var1, i.var2, j.var3}
end
IndexedTable(q)
```
So essentially you are creating an [IterableTable.jl](https://github.com/davidanthoff/IterableTables.jl) with the query, and then you are passing that iterable table to the `IndexedTable` [constructor](http://www.david-anthoff.com/IterableTables.jl/stable/userguide.html#IndexedTables-1) that handles iterable tables.
The [doc](http://www.david-anthoff.com/IterableTables.jl/stable/userguide.html#IndexedTables-1) for that constructor explains what is happening here: the plain constructor will always turn the last column into the data column, and all other columns into index columns. But this constructor also takes some keyword arguments, in particular you can specify which columns should be data and index columns. For example, you could do this:
```julia
IndexedTable(q, idxcols=[:id])
```
And then only the `id` column will be an index column.
You can’t call these constructors that take keyword arguments from the `@collect` statement at this point, so you’ll have to split your query in the way I showed above to make this work.
I have a plan on how to improve this, see [here](https://github.com/davidanthoff/IterableTables.jl/issues/26).
---
### Author:  [@merl-dev](https://discourse.julialang.org/u/merl-dev)
#### Post date: [May 11, 2017, 5:25pm UTC](https://discourse.julialang.org/t/problem-preserving-indexes-using-query-jl-and-indexedtables-jl/3650/3 "2017-05-11T17:25:37Z")
Got it! Thanks.